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AD8348 Scheda tecnica(PDF) 8 Page - Analog Devices |
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AD8348 Scheda tecnica(HTML) 8 Page - Analog Devices |
8 / 13 page PRELIMINARY TECHNICAL DATA Rev. PrF 2/11/03 - 8 - Applications Basic Connections The basic connections described here refer to the AD8348 evaluation board. The schematic for the evaluation board is shown in Figure 1. Power Supply The voltage supply for the AD8348, between 2.7V and 5V, should be connected to the +Vs test point and ground should be connected to one of the GND test points. Device Enable To enable the device, the pin ENBL should be driven to +Vs. Grounding the same pin will disable the device. On the evaluation board this can be achieved by moving SW11 to the ENBL and DENBL positions respectively. VGA Enable The VGA can be enabled by driving the voltage on the pin ENVG to +Vs. In this mode, the MX inputs are disabled and the IF inputs should be utilized. Grounding the pin will disable the VGA and the IF inputs. When the VGA is disabled the MX inputs should be used. On the evaluation board, SW12 should be positioned in either the IF or MX positions. Gain Control When the VGA is enabled, the gain can be controlled by the voltage on pin VGIN. The gain control voltage range is between 0.2 V and 1.2 V. This corresponds to a gain range between 25.6 dB and –18.3 dB. For convenience, a potentiometer R15 is provided to allow for changes in gain without the need for an additional DC voltage source. To use the potentiometer, the switch SW13 must be set to the POT position. Alternatively, an external voltage applied to either the testpoint or SMA connector labeled VGIN can set the gain. SW13 must be set to the EXT position when an external gain control voltage is used. LO Input The local oscillator signal should be fed to the SMA connector J21. This port is terminated in 50 Ohms. The recommended LO drive level is between –10 and 0 dBm. The LO frequency at the input to the device should be twice that of the desired LO frequency at the mixer core. The applied LO frequency range is between 100 MHz and 2 GHz. IF Input The IF input should be fed into the SMA connector IFIP. The VGA must be enabled when this port is used (SW12 in the IF position). MX Input The input to the mixer input can be either single-ended or differential. The evaluation board is, by default, set for single-ended MX drive. To change to a differential drive, T41 should be removed along with resistor R42. DC blocking capacitors (C42, C43) should be installed in place of T41. This will present a nominal differential impedance of 200 Ohms (100 Ohms each side). The differential inputs should then be fed into SMA connectors MXIP and MXIN. Baseband Outputs The baseband outputs are at the IOPP, IOPN, QOPP and QOPN testpoints and SMA connectors. These outputs are not designed to drive 50 Ohm loads directly and should be presented with loads of at least 2k Ohms. Output DC Bias Level The DC bias level of the baseband amplifier outputs are by default tied to Vref through LK11. If desired, the DC bias level can be changed by removing LK11 and driving a DC voltage onto either the VCMO testpoint. AD8348 |
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